How to decode JSON with type convert from string to float64

The answer is considerably less complicated. Just add tell the JSON interpeter it's a string encoded float64 with ,string (note that I only changed the Price definition):

package main

import (
    "encoding/json"
    "fmt"
)

type Product struct {
    Name  string
    Price float64 `json:",string"`
}

func main() {
    s := `{"name":"Galaxy Nexus", "price":"3460.00"}`
    var pro Product
    err := json.Unmarshal([]byte(s), &pro)
    if err == nil {
        fmt.Printf("%+v\n", pro)
    } else {
        fmt.Println(err)
        fmt.Printf("%+v\n", pro)
    }
}

Just letting you know that you can do this without Unmarshal and use json.decode. Here is Go Playground

package main

import (
    "encoding/json"
    "fmt"
    "strings"
)

type Product struct {
    Name  string `json:"name"`
    Price float64 `json:"price,string"`
}

func main() {
    s := `{"name":"Galaxy Nexus","price":"3460.00"}`
    var pro Product
    err := json.NewDecoder(strings.NewReader(s)).Decode(&pro)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println(pro)
}